Bacterial oxidation of dibromomethane and methyl bromide in natural waters and enrichment cultures

Abstract

Bacterial oxidation of 14 CH 2 Br 2 and 14 CH 3 Br was measured in freshwater, estuarine, seawater, and hypersaline-alkaline samples. In general, bacteria from the various sites oxidized similar amounts of 14 CH 2 Br 2 and comparatively less 14 CH 3 Br. Bacterial oxidation of 14 CH 3 Br was rapid in freshwater samples compared to bacterial oxidation of 14 CH 3 Br in more saline waters. Freshwater was also the only site in which methyl fluoride-sensitive bacteria (e.g., methanotrophs or nitrifiers) governed brominated methane oxidation. Half-life calculations indicated that bacterial oxidation of CH 2 Br 2 was potentially significant in all of the waters tested. In contrast, only in freshwater was bacterial oxidation of CH 3 Br as fast as chemical removal. The values calculated for more saline sites suggested that bacterial oxidation of CH 3 Br was relatively slow compared to chemical and physical loss mechanisms. However, enrichment cultures demonstrated that bacteria in seawater can rapidly oxidize brominated methanes. Two distinct cultures of nonmethanotrophic methylotrophs were recovered; one of these cultures was able to utilize CH 2 Br 2 as a sole carbon source, and the other was able to utilize CH 3 Br as a sole carbon source.